The present invention relates to a hermetic compressor and, more particularly, to a joint gas and oil cooling system for a compressor of that type, used in small refrigeration and air conditioning systems.
The hermetic compressors, particularly rotary ones, must be provided with means to cool the electric motor during operation of the unit, order to prevent degradation of the windings insulation and the consequent damage to the electric motor, and with means to cool the lubricant oil, so that it does not warm up excessively thereby degrading and loosing its lubricant properties.
One of the known means to cool the electric motor consists in making the heated refrigerant gas that comes from the compressor discharge to pass through a heat exchanger or pre-cooler to be cooled therein and then to return to the inside of the compressor shell so as to cool the electric motor before being pumped to the refrigeration system.
In spite of cooling the motor, the above mentioned system of the prior art does not cool the lubricant oil. A means employed to perform the joint cooling of gas and oil is described on the patent document U.S. Pat. No. 4,569,645. That document describes a rotary compressor that comprises: a compression chamber; a main bearing and a secondary bearing; a rolling piston that rotates eccentrically, driven by an eccentric shaft inside the compression chamber, defining a high pressure chamber and a low pressure chamber, these elements being assembled inside a sealed shell in the lower portion of which is accumulated the lubricant oil that returns to the shell after being cooled in a heat exchanger external to the shell. During operation of the above mentioned set, the refrigerant gas is compressed and discharged through an ejector tube into a larger-diameter oil feed pipe that is in fluid communication with the lubricant oil stored inside the shell and is connected to the heat exchanger through an extension external to the shell. On being discharged in the oil feed pipe, the refrigerant gas carries the lubricant oil with it, making it circulate through the heat exchanger, where the oil and the refrigerant gas are cooled.
An operational drawback of the previous solution shown above becomes evident at each new start-up of the compressor, when connected to a refrigeration system. As the oil intake is done below the level of the sump, during compressor stops the oil will accumulate in the initial portion of heat exchanger, thereby causing an obstruction to the normal circulation of the gas that should be pumped after each new startup of the compressor.
This periodical pressure loss will, as a consequence, increase the daily power consumption of the refrigeration system. Another drawback of this previous technical solution results fron the manner whereby the oil is collected from the sump. Since the collection is done by drag, the gas ends up being quite diluted in the oil, causing foaming and bubbling, reducing the oil viscosity with a resulting decrease in its lubricant properties and its ability of acting as a sealant against compressed gas leakage between the movable parts inside the cylinder, from the compression chamber to the suction chamber.